KR20050104372A - Liquid absorbing sheet and nonaqueous electrolyte battery pack - Google Patents

Abstract

A liquid absorbing sheet comprising a liquid absorbing resin layer having excellent liquid absorption properties to a nonaqueous electrolytic solution of a constituent nonaqueous electrolyte secondary battery of a nonaqueous electrolyte battery pack (particularly, a lithium-ion nonaqueous electrolyte secondary battery pack) is disclosed. The liquid absorbing resin layer is formed by applying, to a supporting base, a monomer composition containing a monofunctional monomer component (A) containing a monofunctional monomer (a) which can form a homopolymer that is soluble to the nonaqueous solvent of the nonaqueous electrolyte secondary battery and a multifunctional monomer component (B), and irradiating the thus- obtained coating film with ultraviolet light, thereby causing polymerization.

Description

Liquid Absorbing Sheet and Nonaqueous Electrolyte Battery Pack

The present invention relates to a liquid-absorbing sheet for absorbing the electrolyte when leakage of the electrolyte occurs from the non-aqueous electrolyte battery cell in the non-aqueous electrolyte battery pack, and a non-aqueous electrolyte battery pack using the same.

BACKGROUND ART A battery pack in which a plurality of primary battery cells or secondary battery cells and a wiring circuit board are stored in a battery case is widely used. In such a battery pack, when an electrolyte solution leaks from a battery cell, corrosion of wiring of a wiring circuit board may occur, resulting in a poor electrical conduction, or conversely, a short circuit may occur. Therefore, in order to prevent the above problems of corrosion and short circuit even in the event of leakage of the electrolyte, a liquid absorbing member having a liquid absorbent capable of absorbing the electrolyte at or near the contact with the battery cells in the battery pack. Has been proposed (Japanese Patent Laid-Open No. 2001-351588). Here, as the liquid absorbent, various polymer materials of adsorption type, gelation type, and self-swelling type are used. Specifically, polyacrylate absorbent resin, starch-graft copolymer absorbent resin, polyvinyl alcohol absorbent resin, polyacrylamide absorbent resin, isobutyrene-maleic acid copolymer absorbent resin, long chain alkyl acrylate crosslinked polymer, Polynorbornene and the like are exemplified.

However, these liquid absorbents are carbonate-based solvents widely used in non-aqueous electrolyte battery packs, particularly non-aqueous electrolyte secondary batteries constituting lithium ion non-aqueous electrolyte secondary battery packs, whose use has been actively spreading in recent years, For example, there has been a problem that propylene carbonate or dimethyl carbonate cannot be sufficiently absorbed.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems of the prior art, and is excellent in the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery constituting a non-aqueous electrolyte battery pack (especially a lithium ion non-aqueous electrolyte secondary battery pack). It is an object to provide a liquid-absorbing sheet exhibiting liquidity, and to provide a battery pack provided with an electrolyte solution absorbing member formed of such a liquid-absorbing sheet.

1A, 1B and 1C are cross-sectional views of the liquid absorbent sheet of the present invention, respectively.

2 is a perspective view of a non-aqueous electrolyte battery pack of the present invention.

3 is a perspective view of a non-aqueous electrolyte battery pack of the present invention.

It is explanatory drawing of the electrolyte solution absorption test in a simulated battery pack.

Best Mode for Carrying Out the Invention

First, the liquid absorption sheet of this invention is demonstrated.

In the liquid absorbent sheet of the present invention, as shown in FIG. 1A, the liquid absorbent resin layer 1 is formed in a sheet form alone, and as shown in FIG. 1B, a liquid absorbent resin layer ( The aspect in which 1) was formed and the aspect in which the adhesion layer 3 was formed in the side surface of the liquid absorptive resin layer 1 as shown in FIG. 1C are contained. In the case of the aspect of FIG. 1C, a liquid absorptive sheet | seat can be easily installed in a battery case. The adhesive layer 3 is not specifically limited, A well-known adhesive can be used. Moreover, the aspect (without the support body 2 of FIG. 1C) which provided the adhesion layer on one side of the liquid absorptive resin layer without using a support body is also contained in the liquid absorptive sheet of this invention.

Although the adhesive layer 3 is not specifically limited, A well-known adhesive can be used, but it is a liquid absorptivity which shows adhesiveness, considering that the liquid-absorbing resin layer may show adhesiveness and not adhesiveness by composition, as mentioned later. When the resin layer is used as the pressure-sensitive adhesive layer 3, the amount of liquid absorption of the liquid-absorbent sheet can be increased than when the non-absorbent material is used as the pressure-sensitive adhesive layer.

As the support 2 that can be used in the liquid absorbing sheet of the present invention, a resin film which does not permeate the electrolyte solution, for example, a plastic film made of polypropylene or the like can be used, but it can absorb and retain a non-aqueous solvent. It is also possible to use a nonwoven fabric or paper made of plastic fibers such as polypropylene. It is preferable to form the support with such a nonwoven fabric because the absorption rate of the non-aqueous solvent can be increased.

Film formation containing the monofunctional monomer (a) which can form the homopolymer melt | dissolving in the non-aqueous solvent of a non-aqueous electrolyte secondary battery as a liquid-absorbing resin layer 1 which comprises the liquid-absorbing sheet of this invention. The polymer film which superposed | polymerized the said composition to the sheet form by irradiating an ultraviolet-ray to the monomer composition containing the monofunctional monomer component (A) which is a sexual component, and the polyfunctional monomer component (B) which is a crosslinking component is used.

In this invention, it is necessary to use the monofunctional monomer (a) which can form the homopolymer melt | dissolved in the non-aqueous solvent of a non-aqueous electrolyte secondary battery as a monofunctional monomer component (A). This is because when the monofunctional monomer which forms the homopolymer which does not melt | dissolve in such a non-aqueous solvent is used as a monofunctional monomer component (A), the liquid absorption of the resin layer obtained will become inadequate. Herein, the homopolymer dissolving in the non-aqueous solvent means a mixed solvent containing at least one of a non-aqueous solvent (especially, dimethyl carbonate, propylene carbonate and ethylene carbonate, which will be described later, preferably equivalent capacity). Mixed solvent) means that a mass of 10% or more is reduced when 1 part by weight of homopolymer is immersed at room temperature (about 23 ° C.) for 24 hours. The decrease in mass can be determined by comparing the mass after drying of the homopolymer taken out of the non-aqueous solvent after dipping with the mass before dipping. When it melt | dissolves completely, it will become 100% of mass.

The monofunctional monomer (a) is preferably a value obtained by subtracting the solubility parameter value of the nonaqueous solvent of the nonaqueous electrolyte secondary battery applied from the solubility parameter value (SP value (J / cm ³ ) ^1/2 ). Selects from -1.0 to 8.0, more preferably from 2.0 to 6.5. If it is out of this range, the homopolymer will not be substantially dissolved in the non-aqueous solvent, and the liquid absorption of the resulting resin layer tends to be insufficient.

In addition, the solubility parameter can be calculated from the following Fedor equation (see RFFedors, Polym. Eng. Sci., 14 (2), p147, p472 (1947)). The solubility parameter of the monofunctional monomer is calculated for the polymerized repeat units. In the Fedor equation, "σ" is the solubility parameter, "V" is the molar volume (cm ³ / mol), and "Ecoh" is the binding energy (J / mol).

σ = (ΣEcoh / V) ^1/2

Here, as a monofunctional monomer (a), when n mol of monomer (a①) whose solubility parameter value is SP① and m mol of monomer (a②) whose solubility parameter value is SP② are used, The solubility parameter SP (monomer) mixed value is computed from the following formula. The solubility parameter in the case of using 3 or more types of monofunctional monomers together can also be computed similarly.

SP (monomer) mixed value = (SP① × n + SP② × m) / (n + m)

Specific examples of such monofunctional monomers (a) include imide acrylate (SP value = 27.6), N-vinyl-2-pyrrolidone (SP value = 26.2), acryloyl morpholine (SP value = 25), Benzyl acrylate (SP value = 22.9), phenoxyethyl acrylate (SP value = 22.6), N, N-diethyl acrylamide (SP value = 20.6), methoxypolyethylene glycol acrylate (ethylene oxide addition mole number ( n) = 9, SP value = 19.6), methoxypolyethylene glycol acrylate (ethylene oxide addition mole number (n) = 3, SP value = 20.1), tetrahydrofurfuryl acrylate (SP value = 23), phenoxy Polyethylene glycol acrylate (ethylene oxide added mole number (n) = 6, SP value = 20.7), etc. are mentioned. Among them, benzyl acrylate, N-vinyl-2-pyrrolidone, tetrahydrofurfuryl acrylate, and acryloyl morpholine are preferable from the viewpoint of absorbency of the electrolyte solution. These can also use 2 or more types together. Moreover, it is preferable to use benzyl acrylate and acryloyl morpholine together in the balance of the water absorption of a film with respect to electrolyte solution, and film hardness. In the case of using together, the compounding ratio (weight) of benzyl acrylate and acryloyl morpholine is good in absorbing electrolyte solution when there is much acryloyl morpholine, but since a film is hard and it becomes easy to produce a crack, 30/70-70/30 desirable.

On the other hand, the solubility parameter value of the non-aqueous solvent is preferably 17 to 28, more preferably 18 to 23. When out of this range, when used for a lithium battery, there exists a tendency for the cycling characteristics of a battery to fall.

Examples of such non-aqueous solvents include carbonates such as dimethyl carbonate (SP value = 17.4), propylene carbonate (SP value = 20.8), and ethylene carbonate (SP value = 22.5). These may be individual and may use 2 or more types together. Particularly preferred non-aqueous solvents include equal-capacity mixed solvents of dimethyl carbonate, propylene carbonate and ethylene carbonate (SP (solvent) mixed value = 20.2). Also about the solubility parameter of a mixed non-aqueous solvent, it can calculate based on the calculation method of the solubility parameter when a monofunctional monomer is used together based on the solubility parameter of each non-aqueous solvent and the usage-amount (molar number).

The homopolymer of the monofunctional monomer (a) is preferably an ultraviolet polymerization initiator (for example, 2-hydroxy-2-methyl-1-phenylpropane-1- per 100 parts by weight of the monofunctional monomer (a)). On, bisacylphosphonoxide, benzophenone or 2-methylthioxanthone), and 0.1 to 5 parts by weight of the mixture is mixed and irradiated with an energy density of 250 to 350 nm at an energy density of 100 to 2000 mJ / cm ² for polymerization. .

In the present invention, the monofunctional monomer component (A) contains the monofunctional monomer (a) described above, but if it is too small, the amount of liquid absorption of the non-aqueous solvent tends to decrease, so it is preferably contained 20 mol% or more. Do.

In the monofunctional monomer component (A), in addition to the monofunctional monomer (a), other monofunctional monomers such as hydroxyethyl acrylate (SP value = 29.6), acrylic acid ( SP value = 28.7), 2-ethylhexyl acrylate (SP value = 18.9), lauryl acrylate (SP value = 18.7), etc. can also be mix | blended.

In the present invention, the multifunctional monomer component (B) is a component for introducing a crosslinked structure into the liquid absorbent resin layer 1, and preferably a monomer having two or more acrylate residues. For example, hydroxypivalic acid neopentylglycol diacrylate, polyethylene glycol diacrylate (ethylene oxide addition mole number (n) = 14), bisphenol A diacrylate, phenylglycidyl ether acrylate, phenylglycid Dyl ether acrylate, hexamethylene diisocyanate urethane prepolymer, etc. can be used.

If the amount of the polyfunctional monomer component (B) in the monomer composition is too small, the shape preservability of the liquid-absorbing resin layer 1 may be insufficient. If the amount is too large, the crosslinking density may be insufficient. Preferably, it is blended in an amount of 0.0001 to 0.17, more preferably 0.001 to 0.1.

Here, when a crosslinking density makes the number of functional groups in 1 molecule of polyfunctional monomers a, the number of moles of the polyfunctional monomer in a monomer composition is b, and the number of moles of the monofunctional monomer in a monomer composition is c, by the following formula A number that is defined.

Crosslink density = a × b / (b + c)

The liquid-absorbing sheet of this invention apply | coats the monomer composition containing a monofunctional monomer component (A) and a polyfunctional monomer component (B) on peeling films, such as a polyethylene terephthalate film, as mentioned above, and the obtained coating film is ultraviolet-ray When it polymerizes in a sheet form by irradiation and peels from a peeling sheet, the thing of the aspect shown in FIG. 1A can be obtained, and when the said monomer composition is apply | coated and superposed | polymerized on a nonwoven fabric, or it laminate | stacks the thing of the aspect shown in FIG. 1A The thing of the aspect of 1B can be obtained, and the thing of the aspect of FIG. 1C can be obtained by apply | coating forming or laminating | stacking an adhesive further on the liquid-absorbing resin layer of the thing of FIG. 1B.

In the case of using a surface having embossed unevenness on the surface as a release sheet, the liquid-absorbing resin layer surface becomes uneven, and the surface area thereof increases. As a result, the liquid absorption rate of a liquid absorption sheet can be made quick.

The monomer composition containing the monofunctional monomer component (A) and the polyfunctional monomer component (B) is directly applied to the inner surface of the battery case 21 of FIG. 2 without being applied on a release film such as a polyethylene terephthalate film, and here. Ultraviolet rays may be irradiated to form the composition at that position.

As a method of apply | coating a monomer composition to a peeling sheet, a nonwoven fabric, etc., a conventionally well-known coating method, for example, a roll coating method, etc. can be used. Moreover, as an example of ultraviolet-polymerization conditions, the conditions which irradiate the ultraviolet-ray of 250-350 nm wavelength normally at 15-25 degreeC by the energy density of 100-2000 mJ / cm <^2> are mentioned.

In addition, when the liquid absorptive resin layer itself has adhesiveness (as a monofunctional monomer of component (A), tetrahydrofurfuryl acrylate (SP value = 23), benzyl acrylate (SP value = 22.9), phenoxyethyl acrylate) (SP value = 22.6), phenoxypolyethylene glycol acrylate (ethylene oxide addition mole number (n) = 6, SP value = 20.7), or methoxypolyethylene glycol acrylate (ethylene oxide addition mole number (n) = 3, SP value = 20.1)), the liquid-absorbent resin layer itself exhibits adhesiveness, and thus can be directly adhered to the battery pack in the aspect of 1A or 1B without providing an adhesive layer. It is also possible to adhere the liquid absorbent resin layer to the support with a hand roller at room temperature without using it (see Fig. 1B). In addition, in consideration of the fact that the liquid leakage in the cylindrical battery is usually the liquid leakage from the positive electrode, the planar shape of the liquid absorbent sheet is preferably in a donut shape so that it can stick around the positive electrode terminal.

In the present invention, it is preferable to further add a flame retardant (liquid phosphate ester flame retardant, aluminum hydroxide, melamine cyanurate, etc.) to the liquid absorbent resin layer 1 of the liquid absorbent sheet of the present invention. Thereby, flame retardance can be provided to a liquid absorption sheet. In particular, in the case of using a liquid phosphate ester flame retardant as the flame retardant, it is possible to impart flame retardancy to the liquid absorbent resin layer 1, specifically, flame retardancy of V-0, V-1 or V-2 grade of UL-94 standard. Can be. In addition, since the phosphate ester flame retardant is usually liquid at atmospheric pressure from -13 ° C to 250 ° C, preferably within room temperature, excellent adhesiveness can be imparted to the liquid absorbent resin layer 1. When the liquid-absorbent resin layer 1 exhibits adhesiveness, the liquid-absorbent resin layer 1 can be directly adhered to the nonaqueous electrolyte secondary battery pack, so that the adhesive layer does not need to be deliberately installed, and the liquid-absorbent resin layer ( Since the thickness of 1) does not have to be made thin as the thickness of an adhesion layer, the liquid absorption amount of this liquid-absorbing sheet can be prevented from falling. In addition, in the case of using a liquid phosphate ester flame retardant as a flame retardant, even if the liquid absorptive sheet is wet-heated (for example, a treatment for 96 hours in an environment with a temperature of 40 ° C. and a humidity of 90% RH), The insulation resistance value of the liquid absorbing resin layer 1 can be made to preferably not be less than 1 × 10 ¹² Ω.

Liquid phosphate ester flame retardants that can be used in the present invention include bisphenol A bis (diphenyl) phosphate, hydroquinol bis (diphenyl) phosphate, phenyl dixenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, trike Silenyl phosphate, xylenyl diphenyl phosphate, resorcinol bis (diphenyl) phosphate, 2-ethylhexyl diphenyl phosphate and the like. Among them, bisphenol A bis (diphenyl) phosphate, hydroquinol bis (diphenyl) phosphate or phenyl dixenyl phosphate can be preferably used in terms of imparting adhesion.

If the amount of the liquid phosphate ester flame retardant is too small, sufficient flame retardancy cannot be obtained, and even if too large, sufficient flame retardancy cannot be obtained, so that the total amount of the monofunctional monomer component (A) and the polyfunctional monomer component (B) is 100 parts by weight. It is preferably 70 to 200 parts by weight, more preferably 100 to 150 parts by weight.

The liquid-absorbing sheet of the present invention is a non-aqueous electrolyte battery cell, a wiring circuit board, and a non-aqueous electrolyte battery cell in which the electrolyte solution absorbing member for absorbing the electrolyte when leakage occurs when the non-aqueous electrolyte battery cell is provided. It can be used suitably as said electrolyte solution absorption member mentioned above in an aqueous electrolyte battery pack. For example, as shown in FIG. 2, in the battery pack in which the nonaqueous electrolyte battery cell 23 is disposed on the wiring circuit board 22 provided in the battery case 21, the nonaqueous electrolyte battery cell 23 is provided. In the case where leakage of electrolyte occurs from the liquid electrolyte, a liquid absorbent sheet 26 as described in FIG. 1A is disposed between the wiring circuit board 22 and the non-aqueous electrolyte battery cell 23 as an electrolyte absorbing member for absorbing the electrolyte. You may. Here, the nonaqueous electrolyte battery cell 23 and the wiring circuit board 22 are connected by the metal lead 24, and are further connected by the external terminal 25. In addition, as shown in FIG. 3, the liquid absorptive sheet | seat 27 demonstrated by FIG. 1C can also be arrange | positioned on the nonaqueous electrolyte battery cell 23 so that a support body may be the nonaqueous electrolyte battery cell 23 side.

In addition, in FIG.2 and FIG.3, although the shape of the battery case in the nonaqueous electrolyte battery pack was made into a rectangular parallelepiped, and the shape of the battery cell was made cylindrical, it is not limited to these in the nonaqueous electrolyte battery pack of this invention. It can be set as the shape and arrangement structure according to the intended use. In addition, the kind of battery cell is not limited, either.

The non-aqueous electrolyte battery pack of the present invention described above is a monofunctional monomer containing a monofunctional monomer (a) capable of forming a homopolymer dissolved in the non-aqueous solvent of the non-aqueous electrolyte secondary battery as the non-aqueous electrolyte absorbing member material. Since the liquid-absorbing sheet provided with the liquid-absorbing resin layer excellent in the performance which absorbs and retains a nonaqueous electrolyte solution formed from the monomer composition containing a monomer component (A) and a polyfunctional monomer component (B) is used, a battery cell Even when the non-aqueous electrolyte leaks out, corrosion and short circuit occurrence of the wiring circuit can be greatly suppressed.

The present inventors include a monofunctional monomer component (A) comprising a monofunctional monomer (a) capable of forming a homopolymer that is soluble in a nonaqueous solvent of a nonaqueous electrolyte secondary battery, and a polyfunctional monomer component (B). The present invention was completed by discovering that a resin layer obtained by polymerizing the composition in a sheet form by irradiating ultraviolet-rays onto the ultraviolet-polymerizable monomer composition described above can absorb and retain a large amount of an electrolyte solution.

That is, this invention is a liquid absorptive sheet | seat containing a liquid absorptive resin layer, The monofunctional monomer (a) which can form the homopolymer which the said liquid absorptive resin layer melt | dissolves in the non-aqueous solvent of a nonaqueous electrolyte secondary battery is Provided is a liquid-absorbing sheet characterized by polymerizing the composition by irradiating ultraviolet rays to a monomer composition comprising a monofunctional monomer component (A) and a polyfunctional monomer component (B).

In addition, the present invention provides a non-aqueous electrolyte battery provided with an electrolyte absorbing member for absorbing the electrolyte when leakage occurs from the non-aqueous electrolyte battery cell, the wiring circuit board, and the non-aqueous electrolyte battery cell in the battery case. In the pack, there is provided a non-aqueous electrolyte battery pack, characterized in that the electrolyte absorbing member is formed of the above-described liquid absorbing sheet.

Hereinafter, an Example demonstrates this invention concretely.

<Reference Example>

The solubility of the homopolymer made of monofunctional monomer in the nonaqueous solvent of the nonaqueous electrolyte secondary battery was tested as described below.

That is, 1 mass part of photoinitiators (2-hydroxy-2-methyl-1-phenylpropan-1-one; D1173, Ciba specialty chemicals) are added to 100 mass parts of monofunctional monomers, and the obtained mixture is a polyethylene terephthalate film It was apply | coated to the roll coater, and it superposed | polymerized by irradiating the ultraviolet-ray of 365 nm wavelength with the energy density of 2000 mJ / cm <^2> . 1 part by mass of the obtained polymer membrane (monopolymer membrane) was immersed in 300 parts by mass at 23 ° C. for 24 hours in an equal-capacity mixture of dimethyl carbonate / propylene carbonate / ethylene carbonate (SP (solvent) mixing value = 20.2) After the mixture was filtered, the solid remaining on the filter was dried at 100 DEG C for 1 hour, and the solubility (wt%) was calculated by the following formula. The results obtained are shown in Table 1 below. In the formula, W ₁ is a polymeric film mass before immersion, W ₂ is the weight of the solids content.

Solubility = ((W ₁ -W ₂ ) / W ₁ ) × 100

<Examples 1 to 6 and Comparative Examples 1 to 3>

The hydroxypivalic acid neopentylglycol diacrylate as a monofunctional monomer, the polyfunctional monomer shown in following Table 2 and Table 3, 2-hydroxy-2-methyl-1-phenylpropan-1-one as a polymerization initiator are shown in Table 2 And the compounding amounts shown in Table 3. This was apply | coated on the polyethylene terephthalate film by the roll coating method, the ultraviolet-ray of 365 nm wavelength was irradiated at the energy density of 2000 mJ / cm <^2> , and it superposed | polymerized, and the polymerized film was peeled off from the polyethylene terephthalate film, and the single layer liquid absorption sheet was obtained. .

The obtained liquid-absorbent sheet was immersed in a large-capacity dimethyl carbonate / propylene carbonate / ethylene carbonate equivalent-capacity mixed solvent (SP (solvent) mixed value = 20.2) at 23 ° C., and after 2 hours the liquid absorbent resin layer The shape of was visually observed and simultaneously taken out from the mixed solvent, the mixed solvent on the surface was immediately wiped off and the weight was measured to calculate the swelling ratio. The obtained results are shown in Table 2. In addition, the SP value (SP (monomer) value) of a monofunctional monomer, the SP value difference (ΔSP value) with a solvent, the crosslinking density of the liquid absorptive resin layer of a liquid absorptive sheet, and the shape after immersion are also shown in Table 2 and Table 3. Indicated.

From the results of Table 2 and Table 3, the liquid-absorbent sheet of Example 1 had a swelling ratio of 10 times, maintained the film shape even after absorbing and swelling the non-aqueous solvent, and leakage of the electrolyte solution occurred from the non-aqueous electrolyte battery cell. In this case, it was found to be useful as an electrolyte absorbing member for absorbing the electrolyte.

In addition, although the liquid absorptive sheets of Examples 2-6 show the performance of the problem level practically as an electrolyte absorbing member, when the crosslinking density falls from the result of Example 2, the shape after absorbing and swelling a non-aqueous solvent will be It was found that there was a tendency to become gel in film form. On the contrary, from the results of Examples 3 and 6, it was found that when the crosslinking density increased, the swelling ratio tended to decrease. From the results of Example 4, it was found that even when N-vinyl-2-pyrrolidone was used instead of benzyl acrylate as the monofunctional monomer, good results could be obtained. From the result of Example 5, when using together the monofunctional monomer which a homopolymer does not melt | dissolve in a non-aqueous solvent, it turned out that there exists a tendency for a swelling ratio to fall.

On the other hand, from the result of the comparative example 1, when not using a polyfunctional monomer at all, it turned out that a liquid absorptive resin layer is melt | dissolved in a non-aqueous solvent and cannot be used as an electrolyte absorbing member. From the results of Comparative Example 2, it was found that when the SP value of the monofunctional monomer was too large and the homopolymer was not substantially dissolved in the non-aqueous solvent, the swelling ratio was too small to be used as the electrolyte absorbing member. On the contrary, it was found from the results of Comparative Example 3 that even when the SP value of the monofunctional monomer was too small and the homopolymer was not substantially dissolved in the nonaqueous solvent, the swelling ratio was too small to be used as the electrolyte absorbing member.

Example 7 Electrolyte Absorption Test in Simulated Battery Pack

As shown in FIG. 4, the ABS resin box 41 having a length of 7.0 cm × a width of 7.9 cm × a height of 2.3 cm was prepared, and the liquid absorbent of Example 1 having a length of 6.5 cm × 6.5 cm × 100 μm in thickness at the bottom of the box. The sheet 42 was adhered with a commercially available adhesive, three lithium ion batteries 43 were loaded thereon, and a glass epoxy substrate 44 was provided as a circuit board in a portion adjacent to the battery.

Further, a test was performed in which one hole (h) was drilled in the side portion of the center cell of the three cells 43 by an electric drill, and the electrolyte solution leaked therefrom was absorbed into the liquid absorbent sheet. After the hole (h) was left to stand for one day, the inside of the battery pack was observed and it was observed that the glass epoxy substrate was not wet. In addition, since the weight loss amount of the battery in which the hole h was drilled was 2.5 g, and the weight increase amount of the liquid absorbent sheet was also 2.5 g, it was found that all the leaked electrolyte solution was absorbed into the liquid absorbent sheet.

<Examples 8 to 15>

Monofunctional monomer as described in Table 4 below, polyethylene glycol diacrylate as polyfunctional monomer (ethylene glycol addition mole number = 14; 14EG-A, Kyoeisha Chemical Co., Ltd.), 2-hydroxy-2-methyl-1 as polymerization initiator -Phenylpropan-1-one was mixed in the compounding amounts shown in Table 4. This was applied on a polyethylene terephthalate film by a roll coating method, and ultraviolet rays of 365 nm wavelength were irradiated at an energy density of 2000 mJ / cm ² to polymerize, and the polymerized film was peeled off from the polyethylene terephthalate film to form a liquid absorbent sheet of a single layer (210). g / m ² ).

An electrolyte solution prepared by dissolving lithium hexafluorophosphate as 1 mol / L as an electrolyte in an equal-capacity mixed solvent of dimethyl carbonate / propylene carbonate / ethylene carbonate (SP (solvent) mixed value = 20.2) was prepared. 0.2 ml of electrolyte was added dropwise to 0.03 g of the liquid-absorbent sheet prepared above, and the time until completely absorbed by the naked eye was measured. After immersing in a sufficient amount of electrolyte at 23 ° C., the shape of the liquid-absorbent resin layer was visually observed after 3 hours, and was taken out of the mixed solvent, immediately wiped off the mixed solvent on the surface, and the weight was measured to calculate the swelling ratio. . In addition, the swelling degree test was done after heating a liquid absorptive sheet in a wet heat oven (40 degreeC, 90% RH, 96 hours). The results obtained are shown in Table 5 below.

In addition, a 5 cm wide polypropylene nonwoven fabric (Unitica) was adhered to both surfaces of the liquid-absorbing sheet prepared above by hand roller method (23 ° C) or thermal lamination method (80 ° C), and tensile tester (Tensilon, Orientec) 4) was used to measure the adhesive strength in the T peeling mode. Further, the 3 cm wide liquid absorptive sheet prepared above was adhered to the Ni surface by the hand roller method (23 ° C.) or the thermal lamination method (80 ° C.), and T peeling was performed using a tensile tester (Tensilon, Orientech Co., Ltd.). Adhesive strength was measured in mode. The obtained results are shown in Table 5.

Table 5 also shows the SP value (SP (monomer) value) of the monofunctional monomer, the SP value difference (ΔSP value) with the solvent, the crosslinking density of the liquid absorbent resin layer of the liquid absorbent sheet, and the shape after immersion.

From the results of Table 5, the liquid absorbent sheets of Examples 8 to 13 had a difference in the absorption rate of the electrolyte solution at the time of quantitative dropping, but the swelling ratio at the time of immersion was about 8 to 9 times, and the nonaqueous solvent was absorbed and swelled. The film shape was maintained even after that, and it was found that it is useful as an electrolyte absorbing member for absorbing the electrolyte when leakage of the electrolyte occurs from the non-aqueous electrolyte battery cell.

Moreover, although the swelling ratio was small compared with the liquid absorptive sheets of Examples 8-13, the liquid absorptive sheet of Example 14 showed the performance of the level which is satisfactory practically as an electrolyte solution absorbing member. In addition, although the liquid absorption sheet of Example 15 was slow in the electrolyte solution absorption rate at the time of quantitative drop compared with the liquid absorption sheets of Examples 8-13, it showed the outstanding swelling ratio.

In addition, since the liquid absorptive sheet | seat of Examples 8-12 shows the adhesiveness itself, the adhesive layer may not be provided separately. In particular, the liquid-absorbing resin layer of the liquid-absorbing sheet of Example 8 exhibited excellent adhesive properties.

<Example 16 (Experiments a to e), Comparative Example 4 (Experiments f to h) and Comparative Example 5>

The monofunctional monomers shown in Tables 6 and 7 below, urethane acrylates (AH600, Kyoeisha) as polyfunctional monomers, 2-hydroxy-2-methyl-1-phenylpropan-1-one as polymerization initiators (D1173, Ciba Specialty Chemicals), a liquid phosphate ester flame retardant or a solid ammonium polyphosphate flame retardant were mixed in the compounding amounts shown in Table 1 or Table 2. This was applied on a polyethylene terephthalate film by a roll coating method, and was polymerized by irradiating an ultraviolet ray of 365 nm wavelength at an energy density of 2000 mJ / cm ² , and laminating a flame-retardant nonwoven fabric (Nippon Byrin Co., Ltd.) at room temperature with respect to the polymerized film. It peeled from the polyethylene terephthalate film and obtained the liquid absorptive sheet of two-layer structure.

The obtained liquid-absorbing sheet was tested for flame retardancy, adhesiveness, swelling ratio of the electrolyte solution, and insulation as described below.

Flame retardant

About the obtained liquid absorption sheet, flame-retardance test was evaluated according to the UL-94 standard. The obtained results are shown in Table 6 and Table 7. If it is V-0, V-1, or V-2 grade, it will show the flame retardance which is satisfactory practically.

Sticky

A 5 cm wide polypropylene nonwoven fabric (Nippon Byrin Co., Ltd.) was adhered to the exposed liquid absorbent resin layer of the liquid absorbent sheet by the hand roller method (23 ° C.), and a T tester (Tensilon, Orientech Co., Ltd.) was used. Adhesive strength was measured in peel mode. The obtained results are shown in Table 6 and Table 7.

Swelling ratio

An electrolyte prepared by dissolving lithium hexafluorophosphate as 1 mol / L as an electrolyte in an equal-capacity mixed solvent of dimethyl carbonate / propylene carbonate / ethylene carbonate was prepared, and the liquid absorbent sheet was immersed in the electrolyte at 23 ° C. 3 hours later, the electrolyte solution on the surface was wiped off and the weight was measured to calculate the swelling ratio. The obtained results are shown in Table 6 and Table 7.

Insulation

The insulation resistance value (Ω) before and after the wet heat treatment of the liquid absorbent resin layer of the obtained liquid absorbent sheet was measured. The obtained results are shown in Table 6 and Table 7.

From the results of Table 6, it was found that the liquid absorbent sheets of Experiments a to d of Example 16 had good flame retardancy and adhesiveness, swelling ratio was 6 times or more, and excellent insulation characteristics. In addition, in the case of the absorbent sheet of Experiment e, it was comparable to the absorbent sheets of Experiments a to d in terms of flame retardancy, adhesiveness, and swelling ratio, and rather excellent in adhesion. However, it can be said that the level is slightly lower in insulation. However, the change before and after the wet heat treatment was small and the storage stability was excellent.

In addition, in the case of the liquid absorptive sheet of the experiment f to h of the comparative example 4 from the result of Table 7, not only the bisphenol A bis (diphenyl) phosphate was added as a liquid phosphate ester flame retardant, but the addition amount is too little or too much It was found that there was a tendency to not attain the expected flame retardancy at most. In addition, in the case of Comparative Example 5 using a solid ammonium polyphosphate flame retardant, it was found that there was no adhesiveness and the insulation was greatly reduced after the wet heat treatment.

Example 17 Electrolyte Absorption Test in Simulated Battery Pack

As shown in Fig. 4, an ABS resin box 41 having a height of 7.0 cm × a width of 7.9 cm × a height of 2.3 cm was prepared, and the suction of Example 1 having a length of 6.5 cm × 6.5 cm × 100 μm in thickness at the bottom of the box was performed. The liquid sheet 42 was adhered with a commercially available adhesive, three lithium ion batteries 43 were loaded thereon, and a glass epoxy substrate 44 was provided as a circuit board in a portion adjacent to the battery.

Further, a test was performed in which one hole (h) was drilled in the side portion of the center cell of the three cells 43 by an electric drill, and the electrolyte solution leaked therefrom was absorbed into the liquid absorbent sheet. After the hole (h) was left to stand for one day, the inside of the battery pack was observed, and it was observed that the glass epoxy substrate 44 was not wet. In addition, since the weight loss amount of the battery in which the hole h was drilled was 2.5 g, and the weight increase amount of the liquid absorbent sheet was also 2.5 g, it was found that all the leaked electrolyte solution was absorbed into the liquid absorbent sheet.

The liquid absorptive sheet of this invention contains the liquid absorptive resin layer which shows the outstanding liquid absorptivity with respect to the nonaqueous electrolyte solution of a nonaqueous electrolyte secondary battery. Therefore, it is useful as an electrolyte absorbing member of a nonaqueous electrolyte battery pack (especially a lithium ion nonaqueous electrolyte secondary battery pack).

In addition, when a liquid phosphate ester flame retardant is used for the liquid absorptive resin layer of the liquid absorptive sheet of this invention, a liquid absorptive resin layer comprises a nonaqueous electrolyte battery pack (especially a lithium ion nonaqueous electrolyte secondary battery pack). The non-aqueous electrolyte secondary battery not only shows excellent liquid absorptivity and tackiness but also excellent flame retardancy. Therefore, the liquid absorbing sheet of the present invention is useful as an electrolyte absorbing member of a nonaqueous electrolyte battery pack.

Claims (13)

Monofunctional monomer component (A) comprising a liquid-absorbing resin layer, wherein the liquid-absorbing resin layer comprises a monofunctional monomer (a) capable of forming a homopolymer dissolved in a non-aqueous solvent of a nonaqueous electrolyte secondary battery. And a monomer composition comprising a polyfunctional monomer component (B) is irradiated with ultraviolet rays to polymerize the composition. The liquid-absorbent sheet according to claim 1, wherein a value obtained by subtracting the solubility parameter value of the non-aqueous solvent from the solubility parameter value of the monofunctional monomer (a) is -1.0 to 8.0. The liquid-absorbent sheet according to claim 2, wherein the solubility parameter value of the non-aqueous solvent is 17 to 28. The method of claim 1, wherein the non-aqueous solvent comprises at least one of dimethyl carbonate, propylene carbonate and ethylene carbonate, wherein the homopolymer is ultraviolet polymerization per 100 parts by weight of the monofunctional monomer (a) A liquid absorbent sheet which is polymerized by mixing 0.1 to 5 parts by weight of an initiator and irradiating ultraviolet rays. The liquid absorbent sheet according to claim 4, wherein the homopolymer is dissolved in the mixed solvent when 1 part by weight of the homopolymer is immersed in 30 parts by weight of the non-aqueous solvent at room temperature for 24 hours. The monofunctional monomer (a) according to any one of claims 1 to 5, wherein the monofunctional monomer (a) is benzyl acrylate, N-vinyl-2-pyrrolidone, imide acrylate, acryloyl morpholine, phenoxyethyl A liquid absorbent sheet which is an acrylate, N, N-diethyl acrylamide, methoxypolyethylene glycol acrylate, tetrahydrofurfuryl acrylate or phenoxypolyethylene glycol acrylate. The liquid absorptive sheet of Claim 1 whose crosslinking density of a liquid absorptive resin layer is 0.0001-0.17. The liquid-absorbing sheet according to any one of claims 1 to 7, wherein the liquid-absorbing resin layer is formed on a support. The liquid-absorbing sheet according to claim 8, wherein the support can absorb and hold a non-aqueous electrolyte solution. The liquid absorbent sheet according to claim 1, wherein the monomer composition further comprises a liquid phosphate ester flame retardant. The liquid phosphate ester flame retardant according to claim 10, wherein the liquid phosphate ester flame retardant is bisphenol A bis (diphenyl) phosphate, hydroquinol bis (diphenyl) phosphate, phenyl dixenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, trike A liquid absorbent sheet which is silenyl phosphate, xylenyl diphenyl phosphate, resorcinol bis (diphenyl) phosphate or 2-ethylhexyl diphenyl phosphate. The method of claim 10 or 11, wherein the monomer composition comprises a liquid phosphate ester flame retardant in a ratio of 70 to 200 parts by weight relative to a total of 100 parts by weight of the monofunctional monomer component (A) and the polyfunctional monomer component (B). A liquid absorptive sheet to be made. An electrolyte absorbing member is provided in the battery case to absorb the electrolyte when leakage of the electrolyte occurs from the non-aqueous electrolyte battery cell, the wiring circuit board, and the non-aqueous electrolyte battery cell. A non-aqueous electrolyte battery pack, characterized in that formed from the liquid-absorbing sheet according to any one of claims 12 to 12.